Why do computers rot the brain?

[AquaTec]

This is very interesting PUG. One thing i am realizing by talking to you and based on the fact that everybody talks to you. there are people out there that think that if you stay on the "right" side of the NDL line then you are not on a decomression dive. I learen in my PADI OW course some 20 plus years ago that on every dive we are ongassing nitrogen and that we would need to offgas a portion of that prior to surfacing. if we stayed within our NDL then that offgassing would be accomplished with a 60 ft/min ascent rate, therfore a direct ascent to the surface could be made.
That was in the early 80's

What has changed..well now it is taught that a "safety stop" will reduce the chances of DCS greatly and the same with a slower ascent rate. and evidently that you are not on gassing if you stay on the "right" side of the NDL. seem weird that this would be droped. I know i still teach it.

I would like to address some of your points

Even PADI recommends the 15 foot "saftey stop" and it is almost identical in effect to the 30,20,10 (other than lacking effective slowing of ascent from 30 to the surface.)

your method is slightly better as the deeper stops offer a slightly hight Po2 but the padi way is easier for those who don't dive very often.

The saftey stop doesn't create an overhead nor is it required if for some reason the divers must surface. But it is becoming more and more a *rule* and even dive computers are demanding it if certain parameters have been exceeded (ascent rate for example.)

it might be a *rule* but stated in the text *strongly recomended* that you do the stop if air allows for it otherwise surface. I have not heard of a computer requiring this, elaberate please. it makes since though because the tables and computers are based on you ascending from 120 feet in 2 minutes if you do it in one then you need to wait that additional minute

The same holds true for what we call minimum deco of 30,20,10 but we are just being forthright about what it really is... recognizing the truth that all dives are deco dives and that to be safe, stops should be made to allow the body a chance to offgas.

I cant believe that everybody isn't taught this at the begining of their training. it would be interesting to take a pole and see who thinks they are not ongassing N2 during a dive.
The bases for many of my oppositions to your views is based on the fact that it was very basic knowledge that all dives are decompression dives being that you are on gassing N2,

One says, "There is a line (the NDL) and if you do not cross that line then you can omit the safety stop with impunity."

I believe this...[don't know the deffinition of impunity] you can skip the safety stop if you want to [not recomended] there is a point in every dive where the adiquit offgassing of N2 can not be accomplished durring the ascent and therfore stops are required to provide the time and higher pressure gradiant to adiquitly accomplish this. for example 40 feet for 20 minutes or 40 feet for 200 minutes somewhere in that dive it changed from a direct surface dive to a required deco dive. that is the line i am speaking of...they are both decomression dives, above the line you will offgas durring ascent and bellow that line you must do stops

The other says, "There is no such line only an increasing inert gas load that must be dealt with to avoid problems... and you need to be aware that if you omit a portion of your deco you may face consequences... and the more deco you omit the greater the chance of that happening and the greater the consequences."

I agree with all of this, the point your missing is that the line is realy in how you deal with it, not weather it exists or not. above the NDL line, it is delt with by a proper ascent rate....below that line it is delt with by performing deco stops and a proper ascent rate.....both sides of the line are decompression dives. the line is drawn in how it is delt with.

How safe is it for some AOW diver to go out and do a dive to 100' for 20 minutes thinking all the while, "Well I know I'm supposed to do a 15' stop for 3 minutes but as long as I don't cross the NDL I can go ahead an skip it." Maybe they can and maybe they can't.... but thinking that way could get them into trouble.

by skipping the stop he removes one safety factor which is built into the dive planning for him by his training agency [because he can't think for himself] 100 feet for 20 minutes with an ascent rate of 60 feet/min you can surface directly....the padi tables also have an added safety margin built into them, because all of their NDL time where once about 5 minutes longer. the tables are designed for the diver who doesn't think......they are for the ocational diver who simply plans his dive by looking at the tables and saying "if i dive within the NDL and do a proper ascent to the surface that will be fine" and it will be...statistics prove this.... the design of the tables themselves adds another safety factor by teaching a square profile when in fact divers will generaly spend a lot of the dive shallower than the maximum depth planned for in the tables..yet they are maintaining a dive plan as if they are at their max depth for the whole dive.

Or maybe having gotten that fish, run low on air and having crossed the *line* they think, "Oh No!!! Now I am into decompression and I must make my stop!!!" and they try but they run out of air at the stop.

Darwin at work here, we certainly don't want to breed any more of these types of divers.

 

[Scuba]

Probably all the reasons given here for why computers rot your brain can be categorized as misuse and/or lack of fundamental diving knowledge and application.

These shortcomings are not the sole domain of computer users but can all be attributed to dive table users as well.

I will concede that the use of a computer probably creates a greater propensity on the part of many to "rely" on it, with the belief that the computer calculates all the critical information for them, hence they do not need to bother with understanding the science behind it, more so than a table user. But again, this belief is not the sole domain of computers users but can be exhibited by table users as well.

Fundamentally, its an operator issue, not an instrument issue.

So here are some advantages my computer gives me over tables.

1. Ascent rate indicator. (Some indication is better than none)

2. More bottom time. (Dive 100' for 5 min, 3 min ascending to 70' for 10 min., 1 min descending to 75' for 3 min, and so on The computer calculates my actual dive profile and applies it to the tables algorithm in real time) Is there a technique to use with tables that would give similar results?

3. Nitrogen and oxygen meter. (I just completed my shallow stop after a deep dive. I look at my nitrogen meter and it show full green, as opposed to being in the yellow or lesser green load. I prefer to surface with a lesser nitrogen load, so I stay shallow longer as gas permits decreasing my nitrogen exposure. Now I see I have reduced my exposure from full green to 3/4 green and surface.) The same could be achieved without a nitrogen meter, but would you be able to calculate with a fair amount of precision how much your nitrogen load is diminishing? Not intended as argumentative, but an honest question.

 

[rmediver2002]

I have recently changed my opinion on computers to be honest... I thought they had the potential to decrease safety initially. While diving in the military the Navy tables are rigidly adhered to, you use your maximum depth to calculate your table and schedule (most often the work site would actually be your maximum depth anyway, there was not much swimming up and down the water column)

I have been watching many divers recently both experienced and not who know the rules of tables and yet push beyond them because they were only that maximum depth for a small portion of the dive... In effect guessing at the amount of nitrogen they absorbed while shallower. I do not think this is at all isolated instances and have come around to the reality that dive computers may be a safer way for people to dive.

Many of us dive on the weekends and attempt to fit four days of diving into two, I completely understand the desire to spend more time underwater especially with the long transits required to get to a new or intersting dive site. I have often wished I did have a computer to allow me more safe bottom time than the tables allowed...Even if it was just finshing off the remaining air in your tanks on a shallow dive...

This is just an example of an opinion changed from one of contempt for the potential apathy resulting from reliance on a computer to one of acceptance that a more accurate estimate of disolved nitrogen could be obtained by a machine...


Jeff Lane

 

[TCDiver1]

Two cents more for the road. FYI ...

Speaking from a Padi perspective, a dive to 100 feet or deeper for any duration equal or less than the NDL requires a 3 min. safety stop. Tables or computer, it makes no difference.

If diving tables, any dive within three pressure groups of a NDL, requires a safety stop.

A safety stop is recommended for any dive, to any depth, for any duration.

The old leading a horse to water cliche applies here. Not sure tables or computers would make a difference for the divers who won't drink.

 

[MikeFerrara]

As I see it, there is not a DCS/ no-DCS line. However when we look at any decompression model we use to predict the effects of a dive, there is a stop required/no stop required line based completely on the math used by the model. If that stop required/stop not required line proves reliable in testing then we have a line. By definition recreational divers are taught to stay on the no stop required side of the line. The basis for the emergency procedures they are taught are the fact that they can retreat to the surface. Even PADI teaches that there are no garantees and so students are encouraged to not push the limits and that they should do safety stops. IMO, safety stops or (min deco) should not represent a vertual overhead because the statistical risk is small if it is ommitted. Statistical risk, now there is a term for you. We go from little risk to great risk as we go from conservative well done dives to great risk in dives that are done poorly or blow away away the limits or both. As far as I know all agencies teach that off-gassing takes place after all dives. Some divers develope the atitude that if they don't violate their computer/or table they are safe and we all know that that isn't true.

A table lets you see haw close you are to the "limits". A computer can if you use it such but I hear many divers tell me "I wasn"t even in the yellow" or "I was barely out of the green" or "I wasn't even close to the red". These divers can't even tell me how close they were to their NDL, in units of time, or as a percentage. They seem to choose not to consider their profile beyond the color. One color is good the other is bad.

Does computer use rot the brain or computer miss-use? Maybe some of these folks had no brain to begin with.

 

[TCDiver1]

MikeFerrara once bubbled...

Does computer use rot the brain or computer miss-use? Maybe some of these folks had no brain to begin with.

As i said Mike, some divers are very thirsty!

 

[nradov]

Scuba once bubbled...
So here are some advantages my computer gives me over tables.

1. Ascent rate indicator. (Some indication is better than none)

An Uwatec digital bottom timer will show you ascent rate the same as any computer. But in practice this feature is mostly useless: a wrist-mounted instrument moves around too much to give an accurate readout. Also, some computers will beep if you ascend too fast and I consider that just as annoying as a cellular phone ringing in a movie theater.

2. More bottom time. (Dive 100' for 5 min, 3 min ascending to 70' for 10 min., 1 min descending to 75' for 3 min, and so on The computer calculates my actual dive profile and applies it to the tables algorithm in real time) Is there a technique to use with tables that would give similar results?

Yes, there is a technique to use with tables that will give similar results. But why bother? If you're still thinking in terms of "more bottom time" then you've missed the point of this discussion and are still believing the fictions you learned in OW class. In the real world we can stay on the bottom as long as we have gas, and then we just have to do whatever is the correct deco during the ascent. For the sort of dives you're probably doing the correct deco is going to be the same as the minimum deco for that depth. And even if you blow it off completely and go straight to the surface you're likely to escape without significant DCS symptoms, assuming you have no circulatory system shunt and are not bounce diving.

3. Nitrogen and oxygen meter. (I just completed my shallow stop after a deep dive. I look at my nitrogen meter and it show full green, as opposed to being in the yellow or lesser green load. I prefer to surface with a lesser nitrogen load, so I stay shallow longer as gas permits decreasing my nitrogen exposure. Now I see I have reduced my exposure from full green to 3/4 green and surface.) The same could be achieved without a nitrogen meter, but would you be able to calculate with a fair amount of precision how much your nitrogen load is diminishing? Not intended as argumentative, but an honest question.

If you really believe that a dive computer is a "nitrogen meter" then I have a bridge I'd like to sell you. In reality it is just a mathematical model that tries to estimate tissue nitrogen loading but there is no way to test whether the information is really accurate. Remember the difference between accuracy and precision? Those models really break down when it comes to doing multi-level and repetitive dives. And if the goal is preventing DCS then nitrogen loading isn't even the most important issue, it is bubbles we care about. The new VPM and RGBM computers do a better job predicting bubbles but since those models don't capture the full complexity of human physiology they still don't generate optimal profiles.

Hanging out at the shallow deco stops for excessive times doesn't gain you anything; beyond a certain point you'd be better off going to the surface as you can offgas faster there. Just don't jump straight from 15ft to 0; take a few minutes for that last and most crucial phase of the ascent to keep bubbling to a minimum.

 

[Scuba]

nradov,

Yes, there is a technique to use with tables that will give similar results. But why bother? If you're still thinking in terms of "more bottom time" then you've missed the point of this discussion and are still believing the fictions you learned in OW class

I'm thinking in terms of this is where I presently find myself at any point in the dive, where exactly do I stand, so I may eliminate assumptions as much as possible and proceed accordingly. The computer takes a reading of your profile every few seconds and compares it to the algorithm being used. Can you create a graph of your dive profile at any point in your dive with the precision of a computer, all the time? And give an exact deco reading when compared to the tables guidelines?

If you really believe that a dive computer is a "nitrogen meter" then I have a bridge I'd like to sell you. In reality it is just a mathematical model that tries to estimate tissue nitrogen loading but there is no way to test whether the information is really accurate.

Maybe you already bought the bridge. So goes the computers mathematical models, so goes the tables they are based on. Same difference.

And if the goal is preventing DCS then nitrogen loading isn't even the most important issue, it is bubbles we care about.

And just what causes nitrogen bubbles to form?

Good point about the theoretical basis of it all.

Yes, there is a point of diminishing returns by staying shallow, I never said otherwise.

 

[Uncle Pug]

Scuba once bubbled...
Maybe you already bought the bridge. So goes the computers mathematical models, so goes the tables they are based on. Same difference.



And just what causes nitrogen bubbles to form?

Scuba... you are still thinking that it has to be either tables or computers.


As for what causes nitrogen bubbles to form... that is a good question... and micro-nuclei seems to be a good part of the answer.

 

[Scuba]

Computers calculate the tables for us real time during the dive. If not, than you'll have to expand my thinking.

With respect to nitrogen bubbles, that was sarcasm open to misinterpretation. I still seem to think that with no nitrogen you get no nitrogen problems. With an increasing nitrogen load you get an increasing nitrogen problem.